Currently, there is strong evidence linking dietary fat intake to the development of obesity but very little is known about the effects of carbohydrate subtype on this disease. However, recent evidence from both rat and human studies suggest that carbohydrate subtype may have direct effects on lipid metabolism. Dietary carbohydrates consist of simple carbohydrates, or sugars, and complex carbohydrates, or starches. All starch is comprised of two polymers of glucose amylose or amylopectin, in different proportions. Rat data indicates that long-term amylopectin feeding causes insulin resistance relative to amylose feeding. In addition, it has recently been shown that amylose feeding effects adipocyte morphology in rats reducing cell size and increase cell number compared with amylopectin- feeding. Also, low glycemic index diets (amylose) seem to increase HDL- cholesterol compared with high glycemic index diets (amylopectin). The studies proposed in this application aims to determine the effects of long- term amylose/amylopectin feeding on adiposity and metabolic profile. The specific aims are: 1) to define the dose-response relationship between the amylose content of the diet and postprandial glycemic/insulinemic response; 2) to measure adipocyte cell size and number in response to a high amylose diet; 3) to correlate any changes in adipocyte morphology with body composition; 4) to measure insulin sensitivity in response to the amylose content of the diet; 5) to determine the effects of the amylose content of the diet on macronutrient storage and utilization. The optimal amylose content in the diet, as determined by meal tests which define the dose-response relationship between the amylose content of the diet and postprandial glycemic/insulinemic response, will be used in a chronic amylose /amylopectin feeding study. Subjects will be randomly assigned to an amylose- or amylopectin-based diet for 12 weeks in a double cross-over blinded design. One group of subjects will consume an amylose-based diet for 12 weeks followed by a 4 week wash out period and conclude the study with 12 weeks on an amylopectin-based diet. The second group shall receive the two diet phases in reverse order (i.e. amylopectin followed by amylose). At he beginning and end of each diet phase adipocyte cell size and number, body composition, macronutrient oxidation rate, insulin sensitivity, and fasting and postprandial blood lipids, glucose, insulin and leptin concentrations will measured. By using this study to define the role of carbohydrate subtype on adiposity and the metabolic changes associated with obesity, we are moving a step closer to the overall aim of this research which is to develop an "anti-obesity" diet. Such a diet would optimally combine the fat and carbohydrate subtypes which most effectively prevent adiposity and the metabolic changes associated with obesity, we are moving a step closer to the overall aim of this research which is to develop an "anti- obesity" diet. Such a diet would optimally combine the fat and carbohydrate subtype which most effectively prevent adiposity and weight gain.